I think your problem is the way you have the data table structured.
Stack the length and width columns so that all of the length values are in one column and all of the width values are in another column. The stack command will actually create a column called "Label" (the default name) that identifies if it is length 1, 2, or 3. Also, change the Date column to be a Nominal modeling type.
Then in graph builder drag the Length (or Width) column to the Y-axis. Drag the "Label" column to the x-axis. Now drag the date column so that it is INSIDE of the x-axis to create the subgrouping.
I assume that you know how to do the rest, but if more help is needed, please let us know.
Dan Obermiller